The present invention relates to a hydraulic circuit with a self-calibrating device for agricultural or earthmoving machinery.
As well known in the art, both agricultural and earthmoving machines comprise a hydraulic circuit for powering various vehicle-mounted devices, such as the steering assembly, differential, power transmission, shovel lifting and lowering assembly (if any), etc. The hydraulic circuit normally also comprises one or more hydraulic power take-off devices for temporarily connecting off-vehicle devices or implements having hydraulic motors and/or actuators to be driven by the hydraulic circuit of the vehicle.
The hydraulic circuit currently comprises one or more electrically controlled hydraulic distributors which are supplied with a high-pressure fluid and, on command, distribute the fluid to the hydraulic power take-off devices. The circuit further comprises a variable-delivery pump for supplying the high-pressure fluid to the hydraulic distributors, and an electronic central control unit is operable to control the hydraulic distributors in order to regulate the flow of high-pressure fluid from the individual hydraulic power take-off devices.
A major drawback of the above type of hydraulic circuit is the relatively high-cost maintenance involved.
That is to say, each hydraulic distributor comprises one or more electrically operated valves for regulating flow to the hydraulic power take-off devices connected to the distributor. In view of the delicate task performed by the valves, the electronic central control unit is calibrated for each hydraulic device at the vehicle assembly stage to ensure that the high-pressure fluid supply set by the driver of the vehicle for whatever hydraulic power take-off device corresponds exactly with the high-pressure fluid actually supplied by said hydraulic power take-off device.
Problems arise, however, when the electrically operated valves of the hydraulic distributor break down and need replacement. In this case, as opposed to simply replacing the valves, the entire hydraulic distributor must be replaced, and the electronic central control unit controlling the distributors must be re-calibrated. Moreover, calibrating the electronic central control unit is a highly skilled job which can only be carried out at the factory or specially equipped service centers, with obvious consequences in terms of cost.
It is therefore an object of the present invention to provide a hydraulic circuit for agricultural or earthmoving machinery, designed to eliminate the aforementioned drawbacks.
It is a feature of this invention to provide a hydraulic circuit for agricultural or earthmoving machinery in which at least one electrically controlled hydraulic distributor is supplied with a high-pressure fluid and, on command, distributes the high-pressure fluid to at least one hydraulic power take-off. The hydraulic circuit also includes a pump unit for supplying the high-pressure fluid to said hydraulic distributor and a control unit for controlling said electrically controlled hydraulic distributor to regulate the flow of high-pressure fluid through the hydraulic power take-off.
It is another feature of this invention that the hydraulic distributor has at least one electrically operated valve for regulating the passage of the high-pressure fluid to the hydraulic power take-off. The hydraulic circuit includes a self-calibrating mechanism for determining the response curve of the electrically operated valve, and for calibrating the control unit on the basis of the response curve.
It is a further object of this invention to provide a method of calibrating a hydraulic circuit for agricultural or earthmoving machinery.
It is still another feature of the invention that the method includes the steps of:
supplying a gradually increasing current to a single electrically operated valve of an electrically controlled hydraulic distributor of said hydraulic circuit, any eventually other electrically operated valves being left de-energized;
determining the electric current value at which the electrically operated valve begins to open; and
determining, on the basis of the electric current value, the position, in a reference plane, of the response curve associated with the electrically operated valve.
These and other objects, features and advantages are accomplished according to the instant invention in which an agricultural or earthmoving machine includes a hydraulic circuit for one or more electrically operated hydraulic distributors. A pump unit supplys a pressurized fluid to the hydraulic distributors which, in turn, supply the pressurized fluid, on command, to the hydraulic power take-offs of the hydraulic circuit. An electronic central control unit controls the electrically operated valves of the hydraulic distributors to regulate supply of the pressurized fluid to the hydraulic power take-offs. The hydraulic circuit also includes a self-calibrating device for determining, on command, the position, in a reference plane, of the response curves of individual electrically operated valves, so that the pressurized fluid supply set by the driver of the vehicle for any one hydraulic power take-off always corresponds exactly with the amount actually supplied by the take-off.